To Access the LEDs:

Locate the SO-DIMM slot and LVDS video connector. The three troubleshooting LEDs 1, 2, and 3 are located to the right of the LVDS cable connector, under a square of black tape. Peel back the tape to view the LEDs. Note that the LEDs are marked 1, 2, 3 from left to right, as show below. An additional front LED is located in an opening at the center of the right speaker, as shown below.